Moisture-limited electrode active material, moisture-limited electrode and lithium secondary battery comprising the same

ABSTRACT

Disclosed are an electrode active material containing moisture in an amount less than 2,000 ppm per 1 g of lithium metal oxide or moisture in an amount less than 7,000 ppm per 1 cm 3  of the lithium metal oxide, and an electrode containing moisture in an amount less than 2,000 ppm per 1 cm 3  of an electrode mix.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Korean Patent Application No.10-2012-0038925 filed on Apr. 16, 2012, Korean Patent Application No.10-2012-0040130 filed on Apr. 18, 2012 and Korean Patent Application No.10-2012-0041117 filed on Apr. 19, 2012, the contents of each of whichare herein incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a repeatedly chargeable/dischargeablelithium secondary battery, and an electrode active material and anelectrode constituting the lithium secondary battery.

BACKGROUND ART

Depletion of fuel cells has brought about a great increase in price ofenergy sources and increased interest in environmental pollution.Eco-friendly alternative energy sources are a necessity for the nextgeneration. In this regard, a great deal of research into powerproduction methods such as nuclear energy, sunlight, wind power andtidal power is underway and power storage devices for efficientlyutilizing the produced energy also attract much attention.

In particular, regarding lithium secondary batteries, an increase intechnological development and demand associated with mobile equipmenthas led to a sharp increase in demand for lithium secondary batteries asenergy sources. Recently, use of lithium secondary batteries as powersources of electric vehicles (EVs) and hybrid electric vehicles (HEVs)has become popularized and usage thereof is expanding to applicationssuch as auxiliary power supply through grid-realization.

A process for fabricating a lithium secondary battery is broadly dividedinto preparing an electrode material, producing an electrode, producingan electrode assembly and fabricating a battery. The production of theelectrode assembly and the battery is carried out in a dry room with acontrolled humidity, while the preparation of the electrode material andthe production of the electrode are carried out in air.

During preparation of the electrode material and production of theelectrode, moisture absorbed in the electrode material or electrodecauses negative reactions in the battery and thus deterioration inbattery performance. For this reason, removal of moisture is essential.

Lithium titanium oxide (Li₄Ti₅O₁₂) is known as a zero-strain materialundergoing little structural deformation during charge/discharge, whichexhibits considerably superior lifespan, does not cause generation ofdendrites and has considerably superior safety and stability. Inaddition, lithium titanium oxide electrodes are greatly advantageous asthey can be quickly charged within several minutes.

However, lithium titanium oxide absorbs moisture in air. Accordingly, anelectrode fabricated using lithium titanium oxide disadvantageouslygenerates a great amount of gas due to decomposition of moisturecontained therein. This gas deteriorates battery performance.

DISCLOSURE Technical Problem

Therefore, the present invention has been made to solve the above andother technical problems that have yet to be resolved.

It is an object of the present invention to provide a battery whichexhibits improved capacity and lifespan by limiting contents of moisturein metal oxide and an electrode to a within predetermined range.

Technical Solution

In accordance with one aspect of the present invention, provided is anelectrode active material for secondary batteries enabling intercalationand deintercalation of lithium ions, the electrode active materialcomprising lithium metal oxide.

The electrode active material contains moisture in an amount less than2,000 ppm per 1 g of the lithium metal oxide or moisture in an amountless than 7,000 ppm per 1 cm³ of the lithium metal oxide.

The inventors of the present application found that it is difficult toinhibit generation of gas, and in particular, generation of hydrogenand/or carbon dioxide, caused by negative reaction associated withmoisture, when a content of moisture is 2,000 ppm or more per 1 g or7,000 ppm or more per 1 cm³.

Preferably, the electrode active material according to the presentinvention contains moisture in an amount not lower than 100 ppm andlower than 2,000 ppm per 1 g of lithium metal oxide, or moisture in anamount not lower than 350 ppm and lower than 7,000 ppm per 1 cm³ oflithium metal oxide.

Specifically, the electrode active material may contain moisture in anamount not lower than 100 ppm and lower than 2,000 ppm, an amount notlower than 100 ppm and lower than 1,500 ppm, and an amount not lowerthan 100 ppm and lower than 1,000 ppm per 1 g of lithium metal oxide.More specifically, the electrode active material may contain moisture inan amount not lower than 100 ppm and lower than 500 ppm per 1 g oflithium metal oxide.

Moisture content can be determined by measuring moisture content per 1 gof lithium metal oxide or per 1 cm³ of lithium metal oxide in theelectrode active material made of a solid excluding the electrodecurrent collector using a coulmetric Karl Fisher method at 400° C.

As can be seen from the Examples described later, the inventors of thepresent application found that an electrode comprising an electrodeactive material having a limited content of moisture per unit weight orper unit volume and a lithium secondary battery comprising the electrodegreatly reduce generation of hydrogen (H₂). As a result, capacity andlifespan are improved.

A method for controlling moisture content within the range defined aboveis not particularly limited.

In an embodiment of the present invention, moisture can be controlled bydrying the electrode active material at a temperature lower than 300°C., or mixing an electrode mix comprising the electrode active materialand then drying the same at a temperature lower than a melting point ofa binder, or immersing the electrode in a solvent more volatile thanwater and then drying the same at a temperature lower than the meltingpoint of the binder, or immersing an electrode assembly which comprisesa cathode, an anode and a polymer membrane and has a structure in whichthe polymer membrane is interposed between the cathode and the anode ina solvent more volatile than water and then drying the same at atemperature lower than a melting point of the polymer membrane.

The melting point of the binder is, for example, lower than 200° C. andthe melting point of the polymer membrane is, for example, lower than100° C.

Specifically, when the electrode mix is mixed with the volatile solvent,followed by drying, or the electrode is mixed with the volatile solvent,followed by drying, the drying is carried out at a temperature lowerthan 200° C. When the electrode assembly is immersed in the volatilesolvent, drying is carried out at a temperature lower than 100° C.

In a specific embodiment of the present invention, the electrodecontains moisture in an amount lower than 2,000 ppm per 1 g of theelectrode mix.

Specifically, the electrode may contain moisture in an amount not lowerthan 100 ppm and lower than 2,000 ppm, an amount not lower than 100 ppmand lower than 1,500 ppm, and an amount not lower than 100 ppm and lowerthan 1,000 ppm per 1 g of the electrode mix. More specifically, theelectrode active material may contain moisture in an amount not lowerthan 100 ppm and lower than 500 ppm per 1 g of the electrode mix.

The solvent more volatile than water is a solvent having a boiling pointlower than 100° C. and examples thereof include, but are not limited to,diethyl ether, ethanol, methanol, n-propanol, isopropyl alcohol,acetone, n-pentane, ethylene dichloride, methyl acetate, ethyl acetate,acetonitrile, tetrahydrofuran (THF), n-hexane, chlorohexane,chloropentane, carbon tetrachloride, 1,2-dichloroethane,1,2-dichloroethylene, trichloroethylene, methylethylketone and1,2-dimethoxy ethane (DME).

The present invention provides a lithium secondary battery obtained byinserting an electrode assembly comprising a cathode, an anode and apolymer membrane interposed between the cathode and the anode into abattery case, followed by sealing. The lithium secondary battery maycomprise a lithium salt-containing non-aqueous electrolyte.

The lithium secondary battery may be a lithium ion battery, a lithiumion polymer battery or a lithium polymer battery. The cathode or anodemay be fabricated by a method including the following processes.

The method for producing the electrode comprises:

dispersing or dissolving a binder in a solvent to prepare a bindersolution;

mixing the binder solution with an electrode active material and aconductive material to prepare an electrode mix slurry;

coating the electrode mix slurry onto a current collector;

drying the electrode; and

pressing the electrode to a predetermined thickness.

In some cases, the method may further comprise drying the pressedelectrode.

In the process of preparing the binder solution, the binder solution isprepared by dispersing or dissolving the binder in the solvent.

The binder may be any binder well known in the art and, specifically,the binder may be selected from the group consisting of fluorine resins,polyolefines, styrene butadiene rubbers, carboxymethyl cellulose, musselproteins (dopamines), silanes, ethylcellulose, methylcellulose,hydroxypropylcellulose, polyethylene glycol, polyvinyl alcohol, andacrylic copolymers.

The solvent may be selected depending on the type of binder and examplesthereof include organic solvents such as isopropyl alcohol,N-methylpyrrolidone (NMP), acetone, water and the like. The solvent maycomprise the afore-mentioned solvent more volatile than water.

In a specific embodiment of the present invention, a binder solution fora cathode may be prepared by dispersing/dissolving PVdF inN-methylpyrrolidone (NMP). A binder solution for an anode may beprepared by dispersing/dissolving styrene-butadiene rubber (SBR)/carboxymethyl cellulose (CMC) in water.

An electrode mix slurry may be prepared by mixing the electrode activematerial and the conductive material with the binder solution ordispersing the electrode active material and conductive materialtherein. The electrode mix slurry thus prepared is transported to astorage tank and stored prior to coating. The electrode mix slurry maybe continuously stirred in the storage tank in order to prevent theelectrode mix slurry from hardening.

Examples of the electrode active material include, but are not limitedto, layered compounds such as lithium cobalt oxide (LiCoO₂) and lithiumnickel oxide (LiNiO₂), or these compounds substituted by one or moretransition metals; lithium manganese oxides such as compoundsrepresented by Li_(1+y)Mn_(2-y)O₄ (in which 0≤y≤0.33), LiMnO₃, LiMn₂O₃and LiMnO₂; lithium copper oxide (Li₂CuO₂); vanadium oxides such asLiV₃O₈, LiFe₃O₄, V₂O₅ and Cu₂V₂O₇; Ni-site type lithiated nickel oxidesrepresented by LiNi_(1-y)M_(y)O₂ (M=Co, Mn, Al, Cu, Fe, Mg, B or Ga, and0.01≤y≤0.3); lithium manganese composite oxides represented byLiMn_(2-y)M_(y)O₂ (M=Co, Ni, Fe, Cr, Zn or Ta, and 0.01≤y≤0.1), orLi₂Mn₃MO₈ (M=Fe, Co, Ni, Cu or Zn); LiMn₂O₄ wherein Li is partiallysubstituted by alkaline earth metal ions; disulfide compounds;Fe₂(MoO₄)₃; carbon such as non-graphitized carbon and graphitizedcarbon; metal composite oxides such as Li_(x)Fe₂O₃(0≤x≤1),Li_(x)WO₂(0≤x≤1) and Sn_(x)Me_(1-x)Me′_(y)O_(x) (Me:Mn, Fe, Pb, Ge;Me′:Al, B, P, Si, Group I, II and III elements of the Periodic Table,halogen atoms; 0≤x≤1; 1≤y≤3; and 1≤z≤8); a lithium metal; lithiumalloys; silicon-based alloys; tin-based alloys; metal oxides such asSnO, SnO₂, PbO, PbO₂, Pb₂O₃, Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂,Bi₂O₃, Bi₂O₄, and Bi₂O₅; conductive polymers such as polyacetylene; andLi—Co—Ni based materials.

In a non-limiting embodiment of the present invention, the lithium metaloxide is preferably represented by the following Formula (1):Li_(a)M′_(b)O_(4-c)A_(c)  (1)

wherein M′ is at least one element selected from the group consisting ofTi, Sn, Cu, Pb, Sb, Zn, Fe, In, Al and Zr;

a and b are determined according to an oxidation number of M′ withinranges of 0.1≤a≤4 and 0.2≤b≤4;

c is determined according to an oxidation number within a range of0≤c<0.2; and

A is at least one negative univalent or bivalent anion.

The oxide of Formula (1) is represented by the following Formula (2):Li_(a)Ti_(b)O₄  (2)

wherein 0.5≤a≤3 and 1≤b≤2.5.

The lithium metal oxide may be Li_(0.8)Ti_(2.2)O₄, Li_(2.67)Ti_(1.33)O₄,LiTi₂O₄, Li_(1.33)Ti_(1.67)O₄, Li_(1.14)Ti_(1.71)O₄ or the like, but isnot limited thereto.

In a non-limiting embodiment of the present invention, the lithium metaloxide may be Li_(1.33)Ti_(1.67)O₄ or LiTi₂O₄. Li_(1.33)Ti_(1.67)O₄ has aspinel structure which undergoes little change in crystal structureduring charge and discharge and is highly reversible.

The lithium metal oxide may be prepared by a method well-known in theart, for example, a solid phase method, a hydrothermal method, a sol-gelmethod or the like and a detailed explanation thereof is omitted.

The lithium metal oxide may be provided as a secondary particle formedof agglomerated primary particles.

The secondary particle may have a particle diameter of 200 nm to 30 μm.

When the particle diameter of the secondary particles is less than 200nm, a high binder content is disadvantageously required to adhere theelectrode to the current collector due to considerably large surfacearea of the secondary particles. In addition, disadvantageously,negative reaction with the electrolyte is also induced. When theparticle diameter of the secondary particle exceeds 30 it isdisadvantageously difficult to obtain high power due to low diffusionrate of lithium ions.

The lithium metal oxide may be present in an amount not lower than 50%by weight and not higher than 100% by weight, based on the total weightof the anode active material.

When the content of lithium metal oxide is 100% by weight, based on thetotal weight of the electrode active material, the electrode activematerial is composed of only lithium metal oxide.

In addition, in a non-limiting example of the present invention, theelectrode active material may comprise lithium metal oxide having aspinel structure represented by the following Formula (3):Li_(x)M_(y)Mn_(2-y)O_(4-z)A_(z)  (3)

wherein 0.9≤x≤1.2, 0<y<2, 0≤z<0.2;

M is at least one element selected from the group consisting of Al, Mg,Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti and Bi;and

A is at least one negative univalent or bivalent anion.

A maximum substitution amount of A is lower than 0.2 mol %. In aspecific embodiment, A may be at least one anion selected from the groupconsisting of halogens such as F, Cl, Br and I, S and N.

The substitution of the anions improves bonding force to the transitionmetal and prevents structural deformation of the compound, thusimproving lifespan of the battery. On the other hand, when asubstitution amount of the anion A is excessively high (t≥0.2), lifespancharacteristics may be disadvantageously deteriorated due to incompletecrystal structure formation.

Specifically, the oxide of Formula (3) may be lithium metal oxiderepresented by the following Formula (4):Li_(x)Ni_(y)Mn_(2-y)O₄  (4)

wherein 0.9≤x≤1.2, and 0.4≤y≤0.5.

More specifically, the lithium metal oxide may be LiNi_(0.5)Mn_(1.5)O₄or LiNi_(0.4)Mn_(1.6)O₄.

Any conductive material may be used without particular limitation solong as it has suitable conductivity without causing adverse chemicalchanges in the battery. Examples of conductive materials includegraphite such as natural graphite or artificial graphite; carbon blacksuch as carbon black, acetylene black, Ketjen black, channel black,furnace black, lamp black and thermal black; conductive fibers such ascarbon fibers and metallic fibers; metallic powders such as carbonfluoride powders, aluminum powders and nickel powders; conductivewhiskers such as zinc oxide and potassium titanate; conductive metaloxides such as titanium oxide; and conductive materials such aspolyphenylene derivatives.

The electrode mix slurry may further comprise an additive such as afiller, as necessary.

The filler is a component optionally used to inhibit expansion of theelectrode. Any filler may be used without particular limitation so longas it does not cause adverse chemical changes in the manufacturedbattery and is a fibrous material. Examples of the filler include olefinpolymers such as polyethylene and polypropylene; and fibrous materialssuch as glass fibers and carbon fibers.

Coating the current collector with the electrode mix slurry is a processof coating an electrode mix slurry to a given thickness on a currentcollector with a predetermined pattern by passing the electrode mixslurry through a coater head.

Coating the current collector with the electrode mix slurry is carriedout by placing the electrode mix slurry on the current collector andthen homogeneously dispersing the electrode mix slurry using a doctorblade, and coating method includes die casting, comma coating or screenprinting. In addition, the electrode mix slurry may be adhered to thecurrent collector by pressing or lamination after forming the electrodemix slurry on a separate substrate.

There is no particular limit as to the current collector, so long as ithas suitable conductivity without causing adverse chemical changes inthe fabricated battery. Examples of the current collector includecopper, stainless steel, aluminum, nickel, titanium, sintered carbon,and copper or stainless steel which has been surface-treated withcarbon, nickel, titanium or silver, and aluminum-cadmium alloys. Thecathode current collector may be processed to form fine irregularitieson the surface thereof so as to enhance adhesion to the cathode activematerials. In addition, the cathode current collectors may be used invarious forms including films, sheets, foils, nets, porous structures,foams and non-woven fabrics. Specifically, the cathode current collectormay be a metal current collector including aluminum and the anodecurrent collector may be a metal current collector including copper. Theelectrode current collector may be a metal foil, an aluminum (Al) foilor a copper (Cu) foil.

In the drying process, the solvent and moisture present in the slurryare removed in order to dry the slurry coated on the metal currentcollector. In a specific embodiment, the drying may be carried out in avacuum oven at 50 to 300° C.

After drying, the method may further include cooling. The cooling mayinclude slow cooling at room temperature.

After completion of coating, the electrode may be compressed to adesired thickness by passing the electrode between two rolls heated to ahigh temperature in order to improve capacity density of the electrodeand adhesivity between the current collector and the active material.This is referred to as a pressing process.

Before passing the electrode between two rolls heated to hightemperature, the electrode may be pre-heated. In the pre-heatingprocess, the electrode is heated before being added to the roll in orderto improve compression effects of the electrode.

The polymer membrane is a separator to isolate the cathode from theanode. When a solid electrolyte such as polymer is used as theelectrolyte, the solid electrolyte may also serve as the separator.

As the separator, an insulating thin film having high ion permeabilityand mechanical strength is used. The separator typically has a porediameter of 0.01 to 10 μm and a thickness of 5 to 300 μm.

As the separator, sheets or non-woven fabrics, or craft papers made ofan olefin polymer such as polypropylene and/or glass fibers orpolyethylene, which have chemical resistance and hydrophobicity, areused.

Typical examples of commercially available products for the separatormay include Celgard series such as Celgard® 2400 and 2300 (availablefrom Hoechst Celanese Corp.), polypropylene separators (available fromUbe Industries Ltd., or Pall RAI Co.) and polyethylene series (availablefrom Tonen or Entek).

Where appropriate, a gel polymer electrolyte may be coated on theseparator to increase battery stability. Representative examples of thegel polymer may include polyethylene oxide, polyvinylidene fluoride andpolyacrylonitrile.

The electrode assembly may include all electrode assemblies with astructure well known in the art such as jellyroll electrode assemblies(or winding-type electrode assemblies), stack electrode assemblies (orlamination-type electrode assemblies) and stack & folding electrodeassemblies.

In this specification, it will be understood that the stack & foldingelectrode assembly includes a stack & folding-type electrode assemblyproduced by placing a unit cell having a structure in which a separatoris interposed between the cathode and the anode on a separator sheet,and folding or winding the separator sheet.

In addition, the electrode assembly may include an electrode assemblyhaving a structure in which the cathode and the anode are laminated byheat-fusion such that one of the cathode and the anode is interposedbetween separators.

As the non-aqueous electrolyte, a non-aqueous electrolytic solution, anorganic solid electrolyte and an inorganic solid electrolyte may beutilized.

Examples of the non-aqueous electrolytic solution that can be used inthe present invention include non-protic organic solvents such asN-methyl-2-pyrollidinone, propylene carbonate, ethylene carbonate,butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethylcarbonate, gamma-butyrolactone, 1,2-dimethoxy ethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide,1,3-dioxolane, 4-methyl-1,3-dioxene, diethylether, formamide,dimethylformamide, dioxolane, acetonitrile, nitromethane, methylformate, methyl acetate, phosphoric acid triester, trimethoxy methane;dioxolane derivatives, sulfolane, methyl sulfolane,1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives,tetrahydrofuran derivatives, ether, methyl propionate and ethylpropionate.

Examples of the organic solid electrolyte utilized in the presentinvention include polyethylene derivatives, polyethylene oxidederivatives, polypropylene oxide derivatives, phosphoric acid esterpolymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol,polyvinylidene fluoride, and polymers containing ionic dissociationgroups.

Examples of the inorganic solid electrolyte utilized in the presentinvention include nitrides, halides and sulfates of lithium such asLi₃N, LiI, Li₅NI₂, Li₃N—LiI—LiOH, LiSiO₄, Li₂SiS₃, Li₄SiO₄,Li₄SiO₄—LiI—LiOH and Li₃PO₄—Li₂S—SiS₂.

The lithium salt is a material that is readily soluble in theabove-mentioned non-aqueous electrolyte and may include, for example,LiCl, LiBr, LiI, LiClO₄, LiBF₄, LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂,LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li, CF₃SO₃Li, LiSCN, LiC(CF₃SO₂)₃,(CF₃SO₂)₂NLi, chloroborane lithium, lower aliphatic carboxylic acidlithium, lithium tetraphenyl borate and imides.

Additionally, in order to improve charge/discharge characteristics andflame retardancy, for example, pyridine, triethylphosphite,triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphorictriamide, nitrobenzene derivatives, sulfur, quinone imine dyes,N-substituted oxazolidinone, N,N-substituted imidazolidine, ethyleneglycol dialkyl ether, ammonium salts, pyrrole, 2-methoxy ethanol,aluminum trichloride or the like may be added to the non-aqueouselectrolyte. If necessary, in order to impart incombustibility, thenon-aqueous electrolyte may further include halogen-containing solventssuch as carbon tetrachloride and ethylene trifluoride. Further, in orderto improve high-temperature storage characteristics, the non-aqueouselectrolyte may additionally include carbon dioxide gas and may furthercontain fluoro-ethylene carbonate (FEC), propene sultone (PRS),fluoro-propylene carbonate (FPC) and the like.

The lithium secondary batteries according to the present invention maybe used for battery cells as power sources of small-sized devices and asunit batteries of middle- or large-sized battery modules comprising aplurality of battery cells.

Also, the present invention provides a battery pack comprising thebattery module as a power source of a medium or large sized device.Preferably, examples of medium or large sized devices include electricvehicles including electric vehicles (EVs), hybrid electric vehicles(HEVs) and plug-in hybrid electric vehicles (PHEVs), and power storagesystems and the like.

Configurations of battery modules and battery packs, and fabricationmethods thereof are well known in the art and a detailed explanationthereof is thus omitted in this specification.

Effects of the Invention

As apparent from the fore-going, the electrode active material and theelectrode according to the present invention advantageously reducegeneration of hydrogen (H₂) caused by decomposition of moisture andimprove battery performance. Accordingly, the lithium secondary batterycomprising the electrode active material and the electrode exhibitsimproved capacity and lifespan.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a curve showing charge and discharge of batteries of exemplaryExamples 1 and 2 according to the present invention; and

FIG. 2 is a curve showing lifespan of batteries of exemplary Examples 1and 2 according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Now, the present invention will be described in more detail withreference to the following examples. These examples are provided only toillustrate the present invention and should not be construed as limitingthe scope and spirit of the present invention.

Example 1

A solid containing Li(Ni_(0.5)Mn_(1.5))O₄ (BASF Corporation), Super-P(Timcal Corporation) and PVdF (Solef Corporation 6020) at a weight ratioof 95:5:5 was mixed with NMP as a solvent to prepare a cathode slurry.The cathode slurry was coated onto an aluminum foil with a thickness of20 μm to produce a cathode with a load of 1 mAh/cm².

A solid consisting of Li_(1.33)Ti_(1.67)O₄ (Posco ESM Corporation T30)having a limited moisture content of 330 ppm/g, Super-P (TimcalCorporation) and PVdF (Solef Corporation 6020) at a weight ratio of95:5:5 was mixed with a NMP as a solvent to produce an anode slurry. Theanode slurry was coated onto an aluminum foil with a thickness of 20 μmto produce an anode with a load of 1 mAh/cm².

Moisture content can be controlled by drying Li_(1.33)Ti_(1.67)O₄ (PoscoESM Corporation T30) under vacuum at 130° C. for five days. Moisturecontent may be measured at 400° C. using a coulmetric Karl Fishermethod.

A battery was produced using the cathode, the anode and an electrolytecontaining a carbonate electrolyte consisting of EC:DMC:EMC at a ratioof 1:1:1, and 1M LiPF₆ as a salt.

Example 2

A battery was produced in the same manner as in Example 1, except thatLi_(1.33)Ti_(1.67)O₄ (Posco ESM Corporation T30) having a limitedmoisture content of 900 ppm/g obtained by drying at 55° C. for 5 dayswas used as an anode active material.

Example 3

A solid containing Li_(1.33)Ti_(1.67)O₄ (Posco ESM Corporation T30),Super-P (Timcal Corporation) and PVdF (Solef Corporation 6020) at aweight ratio of 83:12:5 was mixed with NMP as a solvent to prepare anelectrode mix slurry. The electrode mix slurry was coated onto analuminum foil with a thickness of 20 μm to produce an anode with a loadof 1 mAh/cm².

Example 4

An electrode assembly including 27 cathode and anode pairs was producedusing the cathode of Example 1, the electrode (anode) of Example 3, anda porous polyethylene membrane (Celgard, thickness: 20 μm).

Experimental Example 1

In order to evaluate moisture content effects on battery capacity,batteries of Examples 1 and 2 were subjected to charge/discharge testingunder 0.1 C charge and 0.1 C discharge conditions. Results are shown inFIG. 1. Example 1 (solid line) having a relatively low moisture contentper unit weight inhibited negative reactions caused by moisture andexhibited an increase in capacity.

Experimental Example 2

In order to evaluate effects of moisture content on battery capacity,batteries of Examples 1 and 2 were charged and discharged 100 times at25° C. under 0.1 C charge and 0.1 C discharge conditions. Results areshown in FIG. 2. Example 1 (solid line) having a relatively low moisturecontent per unit weight inhibited negative reactions caused by moistureand exhibited an increase in capacity.

Experimental Example 3

Moisture contents of an experimental group in which the electrode ofExample 3 was immersed in 1,2-dimethoxy ethane (DME) and was dried undervacuum at 55° C. and 130° C. for 5 days, and of a control group in whichthe electrode was not immersed in 1,2-dimethoxy ethane (DME) and wasdried under vacuum at 55° C. and 130° C. for 5 days were measured at400° C. using a coulmetric Karl Fisher method. Results are shown inTable 1.

TABLE 1 Drying temperature Control group Experimental group  55° C. 840ppm/g 627 ppm/g 130° C. 332 ppm/g 312 ppm/g

Experimental Example 4

Moisture contents of an experimental group in which the electrode ofExample 4 was immersed in 1,2-dimethoxy ethane (DME) and was dried undervacuum at 55° C. for 5 days, and of a control group in which theelectrode was not immersed in 1,2-dimethoxy ethane (DME) and was driedunder vacuum at 55° C. for 5 days were measured at 400° C. using acoulmetric Karl Fisher method. Results are shown in Table 2. Themoisture content was measured based upon the innermost electrode(electrode of Example 3).

TABLE 2 Drying temperature: 55° C. Control group Experimental groupElectrode of 980 ppm/g 822 ppm/g Example 3 Separator 158 ppm/g 132 ppm/g

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

The invention claimed is:
 1. An electrode mix comprising: a binder; andan anode active material containing (a) moisture that is equal to orgreater than 900 ppm and is lower than 2,000 ppm with respect to theanode active material and (b) a lithium titanium oxide that isrepresented by the following Formula Li_(a)Ti_(b)O₄, in which 0.5≤a≤3and 1≤b≤2.5.
 2. The electrode mix according to claim 1, wherein themoisture contained in the anode active material is equal to or greaterthan 900 ppm and is lower than 1,500 ppm.
 3. The electrode mix accordingto claim 1, further comprising a conductive material.
 4. The electrodemix according to claim 1, wherein the lithium titanium oxide isLi_(1.33)Ti_(1.67)O₄ or LiTi₂O₄.
 5. The electrode mix according to claim1, wherein the lithium titanium oxide is provided as a secondaryparticle formed of agglomerated primary particles.
 6. The electrode mixaccording to claim 5, wherein the secondary particle has a particlediameter of 200 nm to 30 μm.
 7. An electrode mix comprising: aconductive material; and an anode active material containing (a)moisture that is equal to or greater than 900 ppm and is lower than2,000 ppm with respect to the anode active material and (b) a lithiumtitanium oxide that is represented by the following FormulaLi_(a)Ti_(b)O₄, in which 0.5≤a≤3 and 1≤b≤2.5.
 8. The electrode mixaccording to claim 7, further comprising a binder.
 9. An anode slurryprepared by mixing the electrode mix of claim 8 with a solvent.
 10. Ananode electrode prepared from the slurry of claim
 9. 11. An anode slurryprepared by mixing the electrode mix of claim 3 with a solvent.
 12. Ananode electrode prepared from the slurry of claim 11.